Concern has been raised over the link between exposure to heavy metal toxins and neurological brain damage associated with learning and behavioral disorders in children. Research shows that exposure to heavy metals such as lead and mercury can impair brain development at very early ages—even at low doses previously deemed harmless.

Children are particularly susceptible to the deleterious effects of heavy metal exposure for several reasons. Their developing nervous systems are more sensitive, their bodies absorb toxins more rapidly, and clear them from the system more slowly, than adults. Also, a child's blood-brain barrier, the natural protective mechanism which blocks harmful substances from entering and damaging the brain, is not yet fully formed.

Professionals working in the field of autism have expressed concern that some autistic children may have been exposed to potentially damaging levels of ethyl mercury, contained in a preservative used in certain vaccinations. Clinical neurobehavioral symptoms of mercury poisoning seem to closely parallel many common symptoms of autism.

In addition, several studies have associated high lead levels in children with autism. Elevated levels of lead in hair, signifying long-term toxic exposure to this heavy metal, have been correlated with increased behavior abnormalities and learning disorders in children. Based on clinicians' observations, antimony, a potential toxin found in some fire retardant materials, is also a possible cause for concern.

It is important to remember that heavy metals are pervasive toxic threats in a child's environment, with air, soil, water and food all potential vectors of exposure. Ultimately, the biochemical individuality of each child may play an important role in influencing whether or not such exposure produces neurological damage. Evidence suggests that autistic children may be less able to detoxify toxic agents they are exposed to from the environment and this inability may predispose the children to suffer neural damage consistent with autistic behavioral traits.